Antiskid brake assembly

ABSTRACT

This invention concerns an anti-skid type automotive vehicle wheel brake cylinder comprising a foot brake pedal, a pneumatic brake booster, a hydraulic master cylinder, a skid sensor, a hydraulic wheel cylinder for each of vehicle wheels and a pressure regulator for the control of hydraulic wheel cylinder pressure in response to an output from said skid sensor. The brake arrangement according to the present invention means are provided for making a selected pair, preferably the rear pair, of the vehicle wheels more liable to invite a skid of the selected wheel pair than the remaining wheels, preferably front wheel pair. The brake boosters is controlled in response to an output skid signal from said skid sensor in the skid suppressing sense and a cut-off valve is provided for the wheel brake cylinders for the remaining vehicle wheels, said cut-off valve being operated for cutting off the hydraulic pressure delivered from said master cylinder to the latter wheel brake cylinders in response to the skid output signal from said skid sensor.

United States Patent Inada et al.

[451 Mar. 21, 1972 [54] ANTISKID BRAKE ASSEMBLY [72] Inventors: MasmaiInada; Tatsuo Hayashi; Katuki Takayama, all of Kariya-shi, Japan [73]Assignee: Aisin Seiki Company Limited [22] Filed: Mar. 24, 1969 [21]Appl. No.: 809,853

[30] Foreign Application Priority Data Mar. 22, 19 68 Japan ..43/18673Oct. 11, 1968 Japan ..43/74037 [52] US. Cl ..303/21 F, 188/181 A, 303/6C,

303/22 R, 303/61 [51] Int. Cl ......B60t 8/04, B60t 8/22, B60t 8/26 [58]Field of Search ..303/21, 22, 61-63, 303/68-69, 6; 188/181; 60/545, 54.5P

[56] References Cited UNITED STATES PATENTS 3,414,334 12/1968 Payne..303/6 C 3,453,029 7/1969 Swanson. ..303/6 C 2,178,290 10/1939 Sorensen..303/21 3,093,422 6/1963 Packer et al... 303/21 3,153,559 10/1964Schaffer ...303/21 3,288,232 1l/1966 Shepherd ..303/21 Walker ..303/21Arentoft et al. Chouings ..303/21 l 5 ABSTRACT This invention concernsan anti-skid type automotive vehicle wheel brake cylinder comprising afoot brake pedal, a pneumatic brake booster, a hydraulic mastercylinder, 21 skid sensor, a hydraulic wheel cylinder for each of vehiclewheels and a pressure regulator for the control of hydraulic wheelcylinder pressure in response to an output from said skid sensor. Thebrake arrangement according to the present invention means are providedfor making a selected pair, preferably the rear pair, of the vehiclewheels more liable to invite a skid of the selected wheel pair than theremaining wheels, preferably front wheel pair. The brake boosters iscontrolled in response to an output skid signal from said skid sensor inthe skid suppressing sense and a cut-off valve is provided for the wheelbrake cylinders for the remaining vehicle wheels, said cut-off valvebeing operated for cutting off the hydraulic pressure delivered fromsaid master cylinder to the latter wheel brake cylinders in response tothe skid output signal from said skid sensor.

8 Claims, 16 Drawing Figures Patented March 21, 1972 3,650,573

5 Sheets-Shout 1 REAR WHEEL BRAKE CYLINDER PRESSURE Patented March 21,1972 3,650,573

5 Sheets-Sheet 2 REAL BRAKE PERFORMANCE CURVE I/O/z IDEAL BRAKEPERFORMANCE CURVE FRONT WHEEL BRAKE CYLINDER PRESSURE FIG. 2

I I FROM BRAKE 4 r A PEDAL 84 840 it. k 71. ivy/5101952047. Wm;

FROM ENGINE 69 79 77 00 INTAKE MANI- I a Wfi I I L L 1 I78 I I". r. I:I: I"; I, L J! I. .I L J I. .I L..J \g

I ENGINE INTAKE 1 I06 MANIFOLD Patented March 21, 1972 v 3,650,573

5 Sheets-Sheet 5 Patented March 21, 1972 3,650,573 5 Sheets-Shoot 4 0+TO BATTERY 52 FIG. 7

' FROM 0.c.

CUWRRENT SOURCE 6E 23 REAL BRAKE 8] PERFORMANCE CURVE mi E a: Y 3 g X Sz 3.; IDEAL BRAKE PERFORMANCE a: o T CURVE FRONT WHEEL BRAKE 1/ CYLINDERPRESSURE TO D.C.

CURRENT SOURCE ll Tlo WHO 70 74 l73b I76 FIG. I O

ANTISKID BRAKE ASSEMBLY This invention relates to improvements in andrelating to the automotive brake system of the antiskid type for vehiclewheels, comprising a foot or the like operated brake actuating meanssuch as a brake pedal, a preferably pneumatic booster, a hydraulicmaster cylinder, a wheel skid sensor, a hydraulic pressure reducingvalve assembly controlled thereby, and a hydraulic cylinder provided foreach of the vehicle wheels.

in the conventional antiskid type wheel brake system of the kind abovereferred to, when generally speaking, the antiskid operation is suchthat the hydraulic pressure supplied to the hydraulic wheel cylinder orcylinders of skidding or skidded wheels are reducingly controlled, whilethe hydraulic brake pressure supplied to the remaining vehicle wheels issimultaneously reduced. This kind of operation results in such drawbacksthat the decelerating effect will be considerably and unfavorablyreduced during the antiskid operation. Thus, the overall brake applyingdistance of the vehicle until it reaches a stop becomes considerablylonger than the ideal brake distance andthe personnel in the runningvehicle will experience sudden and severe physical shocks during thebraking period, on account of a broader variation range of theintentional deceleration for wheel braking. This will further invite aretardation in response by the brake booster on account of thenecessarily increased capacity for temporary release of wheel brakepressure for avoiding dangerous wheel skids.

It is therefore the main object to provide an antiskid type automotivewheel brake system, capable of substantially obviating theaforementioned several conventional drawbacks.

In the antiskid type automotive brake system according to thisinvention, a selected pair of automotive wheels is braked with strongerhydraulic brake pressure supplied from the master cylinder to thecorresponding wheel brake cylinders than that supplied to the respectivewheel brake cylinders attributed to the remaining automotive wheels sothat a skidding or impending locked condition of the selected wheel paircould be brought about earlier than that of the remaining wheels, and inresponse to a skid signal obtained from the skid sensor provided for theselected wheel pair, an air change-off valve is actuated so as tocontrol the action of the brake booster in the skid suppressing sensefor the front and rear wheel pairs. In response to said output signalfrom said skid sensor a cutoff valve provided for the remaining wheelpair is actuated for interrupting the hydraulic connection between saidmaster cylinder and the respective hydraulic brake cylinder means forthe remaining wheel pair so as to maintain the occasionally prevailingpressure in said brake cylinder means.

These and further objects, features and advantages of the invention willbecome more clear as the description proceeds by reference to theaccompanying drawings constituting part of the present specification andrepresenting by way of example several preferred embodiments of theinvention.

In the drawings:

FIG. I is a schematic general arrangement of the first embodiment of theinvention wherein however all the constituting parts are shown in theiroff-service position.

FIG. 2 is an enlarged axial sectional view of a pneumatic brake boosterassembly schematically shown in FIG. 1.

FIG. 3 is an enlarged longitudinal sectional view of a hydraulic mastercylinder assembly shown schematically in FIG. 1.

FIG. 4 is an electronic circuit constituting part of the sensor shown inFIG. 1.

FIG. 5 is an enlarged axial sectional view of a combined hydraulicreducing valve and pneumatic and vacuum changeoff valve assembly shownschematically in FIG. 1.

FIG. 6 is an enlarged axial sectional view of a hydraulic cutoff valveassembly shown schematically in FIG. 1.

FIG. 7 is a front view of a modified main part of the skid sensor whichis constructed in a modified kind of DC motor.

FIG. 8 is a similar view to FIG. 1, illustrating a slight modificationfrom the first embodiment.

FIG. 9 is a further similar view to FIG. 1, illustrating however asecond embodiment of the invention.

FIG. 10 is a longitudinal sectional view of a pneumatic and vacuumchange-off valve assembly shown schematically in FIG. 9.

FIG. 11 is an enlarged axial sectional view of a hydraulic pressurecontrol valve assembly shown schematically in a rectangular block withchain-dotted lines in FIG. 9.

FIG. 12 is an enlarged axial sectional view of a hydraulic load sensingvalve assembly adapted for use in place of the pressure control valveshown in FIG. 1 1.

FIG. 13 is a characteristic curve of the pressure control valve shown inFIG. 11 and expressed in terms of the rear wheel hydraulic cylinderpressure plotted against that for the front wheels.

FIG. 14 is a similar view to FIG. 13, showing a characteristic curve ofthe load sensing valve shown in FIG. 12.

FIG. 15 at (A), (B) and (C) shows several enlarged schematic sectionalviews of a booster control valve fitted in the booster assembly shown inFIG. 2.

FIG. 16 is a schematic wiring connection of a signal processing circuitdelivered from the electromagnetic skid sensor shown in FIG. 7.

Referring now to the drawings, especially FIGS. 1-7, the firstembodiment of the invention will be described in detail.

In FIG. 1, numeral 10 denotes a conventional automotive foot-actuatedbrake pedal, one end 10a of which is pivotably mounted on a suitablyselected part of the automotive chassis, not shown. A pusher rod 11 ispivotably connected at its one end to an intermediate point at 10b.There is provided a return spring 12 acting to return the foot pedal 10from its working position shown in chain-dotted line to its off-serviceposition shown in full line when operator's foot pressure has beenreleased. This spring is tensioned between the chassis or the like rigidmember, not shown, and said pivotable connection at 10b.

Numeral 13 denotes generally a known pneumatic booster assembly which isso arranged as conventionally to provide a boost-up operational outputsubstantially in direct proportion to occasionally applied foot pressureby the operator on the pedal, said pressure being conveyed therefromthrough said pusher rod 11 to the booster 13 in the form of its input. Aconventional hydraulic master cylinder assembly generally shown at 14 ismechanically connected in tandem with the booster, as will be more fullydescribed with reference to FIG. 3.

Master cylinder 14 is formed with two output ports 15 and 18, the formerport being connected through a conduit 16 to the inlet port 17a of ahydraulic cutoff valve assembly, generally shown at 17. Another outletport 18 of the master cylinder 14 is connected through a conduit 19 tothe inlet 21 of a reducing valve assembly 20. The cutoff valve is shownmore in detail in FIG. 6, while the reducing valve 20 is shown in FIG.5. Cutoff valve assembly 17 is formed with an outlet 22 which is kept inhydraulic communication by conduit 23 with a connecting piping 24, theboth ends of the latter being connected to respective wheel cylinders 27and 28 for automotive front wheels at 25 and 26, respectively, onlyschematically shown in FIG. 1. Reducing valve 20 is formed with outletport 29 which is hydraulically connected through a common conduit 30 toa connecting piping 31, the both ends of which are connected torespective wheel cylinders 34 and 35 of automotive rear wheels 32 and33. On account of the very popularity, wheels cylinders 27 and 28, 34and 35 are shown in a highly simplified way by respective blocks.

The assembly 20 is provided with an air change-off valve 36 which isshown in FIG. 5 more in detail.

A rectangular block 37 represents schematically a conventionalautomotive drive engine which is mechanically connected throughreduction gearing 38 shown again only in a block, to a conventionaltransmission 39, the output therefrom being transmitted to a propellershaft 40. The output end of the shaft 40 is mechanically connected to adifferential gearing 41, as is conventionally done. The gearing 41 isdesigned and arranged to be attached to a hollow shaft 42 a moredetailed representation in FIG. 4. This sensor is electrically connectedthrough a lead 44 to an electronic signal processing circuit 45 which isshown in a block in FIG. 1, yet in a more specific way in FIG. 16.

The sensor 43 is designed and arranged to sense a ready-forlocking stateof the rear wheels 32 and 33 when a sudden and heavy braking action isapplied thereto, as will be more fully described hereinafter. Switchingmeans 101 embodied in the electronic circuit is connected through a lead46 to junction point 47 which is connected through lead 49 to relay coil50 and a capacitor 51 connected in parallel thereto. The positive sideof current source 52 is connected through a lead 53 including a junctionpoint 54 to the electronic circuit 45. Junetion 54 is connected througha lead 55 to switch arm 56 cooperable with stationary contact 57, saidelements 55, 57

constituting a normally open switch as shown. Stationary contact 57 isconnected through a lead 102 to one end of solenoid coil 58 adapted foractuation of cutoff valve 17 when energized, while the opposite end ofthe coil is earthed through lead 59. Switch arm 56 constitutes relaycontact of relay coil 50. With the latter energized, the relay contactis brought into its closed position. A self-holding circuit 60 for therelay coil is constituted by switching elements 56, 57; relay coil 50;and capacitor 51. v

One end of relay coil 50 is earthed through junction point 61 whichleads to capacitor 51, and further through a lead 62.

The negative side of current source 52 is earthed through a lead 63. Oneend of actuating coil 64 is connected through a lead 48 to junctionpoint 47, while the opposite end of the coil is connected through a lead65 to earth. As will be described hereinafter, the arrangement shown inFIG. 1 and its related figures is so designed and constructed that therear wheels will be brought into an impending locked condition inadvance of an impending lock condition of the front wheels.

Next, referring to FIG. 2, the design and arrangement of the constituentparts of the booster 13 will be described.

In FIG. 2, numeral 66 denotes an air intake pipe which is open at itslower end to open atmosphere and rigidly connected with a sleeve 67 bymeans of a part of boot-like member 68 made of an elastic substance suchas rubber, said member comprising an undulating tubing 68a which isfixedly attached with its inner end to a sealing member 69 of ringshape. This member 69 is kept in relatively slidable contact with thetubular extension at 70a of a conventional power piston 70 provided witha resilient diaphragm 72 the peripheral edge of which is kept in fixedposition by being positively squeezed by two confronting housingelements 71 and 73 consisting in combination, a stationary housing,generally shown at 103, of the brake booster 13. As seen, the interiorspace of the housing 103 is divided by the diaphragm piston into twochambers of which the right-hand side chamber 74 provides a variablepressure one, while the lefthand side chamber 75 provides a vacuum one,as will become more clear as the description proceeds. The latterchamber 75 is connected through a communication piping 104 to a suitablevacuum source 105 preferably the intake manifold of the drive engine, asschematically shown in FIGS. 2 and 5, although the source has beenomitted from FIG. 1 for simplicity. There is provided a return coilspring 76 abutting between the housing wall 73 and the diaphragm piston70.

A resilient tubular valve member 78 is fixedly attached with its outerend through tongue-and-groove connection 79 with the inner end of acup-shaped supporting member 77 which has been pressure fit into thelongitudinal bore of cylindrical piston extension 70a for performingunitary motion therewith. For assuring this unitary combination of theboth, there is provided a perforated spring disc clip 80.

The pusher rod 11 extends from outside axially and horizontally into theinterior of the booster assembly, the free end 1 1a being received in adeep recess 81a formed in a slidable valve seat member 81 mounted by thepower piston 70, yet being slidable relative thereto. Valve seat member81 is urged in the right-hand direction in FIG. 2 by the provision of anurging spring 82 through spring mount 83 which is fixedly attached tosaid member 81, while the opposite end of said spring abuts .against thepower piston. Under normal or off-service conditions of the brakesystem, valve member 78 is kept in pressure contact with inner valveseat at 81b formed on the member 81, as most clearly seen from FIG. 15at (A). The left-hand end of the valve seat member 81 is telescopicallyreceived in a longitudinal bore 84a formed in the output shaft 84 of thepower piston.

Outer valve seat 85 is formed directly on the power piston, as mostclearly seen in FIG. 2, said seat being normally kept in a separatedposition from the elastic valve member 78.

The left-hand chamber 75 is kept permanently in vacuo through theconnection piping 104 to the suction manifold 105 so far as theautomotive engine rotates. As conventionally, the right-hand chamber 74is also kept in vacuo through pneumatic communication with the vacuumchamber 75, as clearly understood by watching a series of small arrowsshowing the pneumatic communication therebetween. Therefore, thenegative pressures prevailing in both chambers 74 and 75 are practicallysame, and thus, the power piston 70 is urged to the right-hand directionin FIG. 2 under the action of main spring 76.

When the vehicle driver pushes the brake pedal 10 inwards for actuatingthe brake system, pusher rod 11 is urged to move I in the left-handdirection in FIG. 2 so that the valve seat member 81 is also urged tomove in unison with the pusher rod. In the course of this brakeactuating operation, the valve member 78 permanently being urged by anactuating spring 87 is brought into engagement with the outer valve seat85, thereby interrupting the otherwise established pneumatic connectionbetween both chambers 74 and 75. This operating condition corresponds tothat shown in FIG. 15 at (B). With further advancement of pusher rod 11,the valve seat member 81 is moved in the same direction as before, yetbeing brought into separation from contact with the valve member 78, asshown in FIG. 15 at 0 Since the atmospheric pressure coming from airintake pipe 66 and prevailing around the pusher rod as clearlyunderstood at a glance of the right-hand part of FIG. 2, atmospheric airwill flow through the now opened inside valve opening 88 between 78 and81b and a communication passage 89 into the variable pressure chamber74, thus power piston 70 being pneumatically urged to move leftwards inFIG. 2 against the action of main spring 76. Motion is therefore,transmitted from the power piston through its output shaft to masterpiston for actuating the hydraulic brake system with a boosted-upbraking effort as conventionally.

It will be easily understood that all the working parts of boosterassembly 13 are brought back into the normal position shown in FIG. 2,when the operator's foot pressure is released from pedal 10.

Next, referring to FIG. 3, the construction and operation of mastercylinder assembly 14 will now be described.

The assembly 14 comprises a stationary cylinder 90 in which a firstpiston 91 and a second piston 92 are slidably and sealingly mounted. Thecylinder 90 is formed integrally with an oil reservoir 99 containing apool 110 of liquid, preferably oil.

First piston 91 is formed with end flanges 91a and 91b, a circularring-shaped space being formed therebetween and kept permanently incommunication through an opening 1 1 1, bored through the cylinder wall,with the oil pool 110. Between both pistons 91 and 92, there is formed achamber 94 which is normally kept in communication through acompensation port 112, equally bored through the cylinder wall, withsaid oil pool. In addition, a spring 93 is housed in the intermediatechamber 94 and abuts with its both ends against the opposing end facesof the both hydraulic pistons. The

chamber 94 is permanently kept in communication with the output port 18.

Second piston 92 is formed with an end flange 92a and further with apair of separated collars 92b and 92c. Sealing means 114, 115 and 116are provided for effective sealing at the respective flange and collars92a, 92b and 92c. In the similar way, the first piston 91 is also formedwith sealing means 112 and 113. Around the second piston, there isformed an air chamber 96 between flange 92a and intermediate collar 92c,said chamber 96 being permanently kept in communication with ambientatmospheric air through communication passage 117 bored through thecylinder wall. Between both collars 92b and 92c, there is a hydraulicchamber 97 around the second piston 92 which is kept normally through acompensation port 118 with said oil pool 110. A stationary stop 109 isprovided through the cylinder wall so as to protrude into the cylinderspace for limiting the rightward movement of the second piston 92. Afurther compensation port 119 is bored through the cylinder wall fornormal establishment of hydraulic communication between the end space 98and the oil pool 110, said end space being formed between the left-handend wall of the cylinder assembly and the right-hand end of secondpiston 92 and containing a return spring 107 abutting against the both.The output port is formed through the cylinder end. A cover 108 isprovided for avoiding possible invasion of foreign dust and the likeparticles into the inside space of the oil reservoir. The lefthand oractuating end of output shaft 84 is received under pressure in a deepconical recess 91c formed axially in the first piston, for transmittingthe brake actuating effort coming from the foot pedal 10 through thebooster assembly and its output shaft 84, to the first piston 91.

When the output shaft 84 of booster power piston 70 is actuated to movein the left-hand direction in FIGS. 2 and 3, as

described by reference to FIG. 2 hereinbefore, the first piston 91 ismoved leftwards in FIG. 3 so as to compress the spring 93 and tointerrupt the hydraulic communication between movable and variablehydraulic first chamber 94 and the oil pool 110. The simultaneouslycompressed oil in the chamber 94 is delivered therefrom through port 18,conduit 19, inlet 21, outlet 29, piping 30, 31 to the wheel cylinders 34and 35 for braking the rear wheels 32 and 33. At this stage, thereducing valve assembly is not actuated, so far as any skidding orreadyfor-skidding condition of the rear wheels is not sensed. With asmall time lag from the actuation of said first piston, the secondhydraulic piston 92 is moved leftwards for interruption of the hydrauliccommunication between chamber 98 and oil pool 110 through secondcompensation port 119, and then compress the oil contained therein. Thethus compressed oil is delivered from the chamber 98 through outlet port15, conduits l6 and 23 and piping 24 to front wheel cylinders 27 and 28for braking the front wheels. At this stage, cutoff valve assembly 17 isno brought into operation when there is not indication ofready-for-skidding or actual locked condition of the front wheels.

It will be easily understood that when the drivers foot pressure isreleased from foot pedal 10, all the working parts of master cylinderassembly 14 are returned to their non-working position shown in FIG. 3.

The skid sensor shown in FIG. 1 at 43 is illustrated in more detail inFIG. 4. In FIG. 4, G denotes a conventional DC generator andits negativeoutput terminal is connected electrically to resistor R1. C1 is acharging condenser; C2 is a differentiating capacitor; C3 a delaycondenser; D1 a diode; Trl a transistor; R2 a resistor; V denotes anelectromagnetically operating changeover valve assembly which isschematically shown at36 in FIG. 1 and more in detail in FIG. 5; RL]denotes a relay coil which is designed and arranged so as to controlnormally opened relay contacts a and b which constitutes in combinationthe switch 101 in FIG. 1. All these circuit elements are mutuallyconnected as shown in FIG. 4 so that the connecting mode can be easilyunderstood without further analysis.

The skid sensor, or more precisedly, generator G, is mechanicallyconnected with transmission 39 so that the rotating conditions of rearwheels are sensed by the generator, although the connecting mode hasbeen omitted from the drawings for simplicity and on account of itspopularity.

Under running condition of the rear wheels 32 and 33, a negative voltagerelative to the earth potential and depending upon the occasionalrotational speed of the rear wheels is delivered from the negativeoutput terminal of generator G through resistor R1 to junction pointleading to condensers Cl and C2.

When the brake is applied to the rear wheels, the voltage appearing atthe junction 120 varies and a positive voltage will appear at junctionpoint 121 which leads to condenser C2, diode D1 and the base electrodeof transistor Trl. This positive voltage is amplified through thetransistor and the amplified current is conveyed to relay coil RL 1.When a sudden and heavy braking action is applied to the rear wheels tosuch a degree that these wheels are brought into nearly or practicalskidding conditions, the contacts a and b of relay switch 101 arethereby closed and the air changeover valve 36 is actuated so as toreduce the hydraulic pressure supplied to wheel cylinders 34 and 35, aswill be more fully described by reference to FIG. 5 hereinafter.Condenser C3 provides a time lag, for instance, of 0. 10.2 second forkeeping the relay contacts closed even when the wheel speed reduction isrecovered instantly.

When the rear wheel speed is recovered on account of said reduction inthe hydraulic wheel cylinder pressure, the poten tial at junction 121will becomes zero, and thus, the transistor Trl turns off.

The reducing valve assembly 20 is shown more in detail in FIG. 5. Thisassembly comprises a stationary housing consisting of two housingelements 201 and 202 rigidly connected together at 203. The main part ofthe interior space of the housing is divided into two chambers 204 and205 by the provision of a diaphragm piston 222. Vacuum inlet socketcommunicating with chamber 205 is pneumatically connected through aconduit 207 to the engine suction manifold 105.

From vacuum chamber 205 extends a conduit 208 to a passage 210 keptnormally in pneumatic communication with valve chamber 228 which leadsthrough a further passage 221 to variable pressure chamber 204. Thus,under normal conditions, vacuum pressure prevails in both chambers 204and 205. An auxiliary housing 229 is fixedly attached to main housingelement 201 and houses solenoid coil 64 wound around a bobbin 214fixedly mounted within the auxiliary housing and adapted for actuating aplunger 212. The plunger 212 has an extension 212a which is formed witha valve member 215 covered with a resilient layer 216 made of rubber orthe like resilient material. The valve member 215 is designed andarranged so as to close a valve seat 217 defining one end of a space 211formed within the main housing element 201 and communicatespneumatically with a passage 218 which leads through an inlet piping 219and air cleaner 220 attached to the free end thereof, to the openatmosphere. Return spring 213 is tensioned between bobbin 214 andplunger 212 so as resiliently to urge the latter to move in theleft-hand direction in FIG. 5. The passage 210 is defined at itsinnermost end by a further valve seat 231, said valve member 215 beingbrought into contact with this valve seat 231 when the solenoid coil 64is energized, said coil having electrical leads 48 and 65 which are alsoshown in FIG. 1.

A bore 230 is formed within main housing member 201 and receivesslidably and sealingly a plunger 222a of diaphragm piston 222, saidplunger being formed with a reduced extension 223. A valve chamber232'is hydraulically connected with said bore 230 and houses movably afree valve member 224 which is normally kept in pressure engagement withthe free or left-hand extremity of said reduced extension 223 under theinfluence of a return spring 225 housed within said valve chamber 232from which the conduit 19 extends to output port 18 from the mastercylinder 14. The conduit 30 communicates with the interior of bore 230and there is established normally a free hydraulic communication betweenboth conduits 19 and 30, because of the normal separation of valvemember 224 from valve seat 233 adapted for on-off controlling thehydraulic communication between valve chamber 232 and bore 230, thenceto conduit 30. In the vacuum chamber 205, there is provided a main orreturn spring 227 adapted for urging the diaphragm piston 222 towardsleft in FIG. 5.

Under normal or off-service conditions wherein there is no tendency forinviting skidded conditions of the rear wheel brake system,substantially equal vacuum pressures prevail in both chambers 204 and205. Under the influence of main return spring 227, the diaphragm piston222 is kept in the position shown in FIG. 5. Since the solenoid coil 64is deenergized, plunger 212 is kept in the shown position, thus thevalve member 215 is kept in contact with valve seat 217 under theinfluence of return spring 213. Therefore, atmospheric pressure suppliedfrom ambient atmosphere through air cleaner 220 and intake conduit 219is conveyed through passage 218 into the space 211 the extremity ofwhich is defined by valve seat 217 which is kept in closed position, asabove stated.

When the foot pedal 10 is actuated in the manner described hereinbefore,pressure oil is conveyed from the master cylinder 14 through conduit 19,valve space 232, valve seat opening 233 and bore 230 to conduit 30 whichleads through the piping 31 to rear wheel cylinders 34 and 35, as wasbriefly described hereinbefore.

When the skid sensor 43 senses a ready-for-skidding or practicallyskidded condition of the rear wheels 32 and 22, current will be conveyedfrom DC generator G contained in the sensor 43 via now closed switch 101to the changeover valve 36, more specifically solenoid coil 64 which isnow energized. By this energization, plunger 212 advances rightwards inFIG. 5, thus valve member 215 being brought into pressure contact withvalve seat 231 and thereby pneumatic communication between both chambers204 and 205 being interrupted, while atmospheric pressure air isconveyed through the now opened valve seat 217, valve chamber 228 andpassage 221 into the left-hand vacuum chamber 204. On account of thethus established pressure difference between both chambers 204 and 205,diaphragm piston 222 is urged pneumatically to move rightwards in FIG.5, thereby plunger 222a and its extension 223 moving in unison therewithand valve member 224 closing the valve seat 233. In this way, hydrauliccommunication between ducts l9 and 30 is interrupted. With furtheradvancing or righward movement of plunger 222a, the effective volume ofbore 230 is increased, thus the hydraulic pressure prevailing in wheelcylinders 34 and 35 being correspondingly reduced.

When the skidding or skidded conditions of rear wheels are removed inthe foregoing way and solenoid coil 64 is deenergized, all theconstituent parts of the assembly shown in FIG. 5 are returned to theirnormal position shown therein.

Cutoff valve assembly 17 is shown in FIG. 6 more in detail. Thisassembly comprises a main body 123 is formed therein with a valvechamber 124 in which a valve member 126 is provided and backed up withan actuating spring 125 urging the valve member in closing direction.The valve member has a spirally grooved stem 126 slidably guided througha guide passage 127 formed horizontally in the main body 123 and abutsagainst a plunger 128 backed-up by a return spring 129, the opposite endof the latter abutting in turn against a stationary core piece 130. Theplunger 128 is slidably guided in a sleeve 13] which is rigidly attachedto the core piece 130 by press-fiting or the like conventionalpositioning means. Around the sleeve 131, there is mounted a bobbin 132made of suitable plastic material and mounting a solenoid coil 58 fromwhich leads 59 and 102 shown in FIG. 1 extend. For effective positioningthe solenoid assembly 132, 58, there is provided a positioning ring 134is inserted between the main body 123 and the core piece 130. As shown,the core assembly and the positioning ring are housed in and positionedin place by a cover member 135. The pipe 23 is hydraulically connectedwith the valve chamber 124 by means of a conventional pipe fitting means136. In the similar way, the conduit 16 is connected with the up-streampart of the valve chamber in advance of valve seat member 138, by meansof a conventional pipe fitting means 137. The length of valve stem 126ais so selected that under normal conditions the valve member 126 is keptin separation from the valve seat member 138 as shown.

When the relay switch 101 is closed, as was referred to hereinbefore byreference to FIG. 4, current will now flow from battery 52 through lead53, junction 54, switch 101, lead 46, junction 47, lead 49, relay coil50, junction 61, lead 62 to earth, thence back to the battery (see, FIG.1). Upon energization of relay coil 50, relay contact 56 is brought intocontact with stationary contact 57, thus current now flowing from thebattery 52 through lead 53, junction 54, lead 55, now closed relayswitch 56, 57 and lead 102 to solenoid coil 58 which is thus energized.By the energization of the coil 58, plunger 128 is attracted to corepiece 130 against the action of return spring 129 and valve member 126together with its stem 126a will follow after the movement of theplunger, thereby the valve being brought into its closed position andabutting against valve seat member 138 under the influence of its backupspring 125. Therefore, otherwise established hydraulic communicationbetween conduits 16 and 23 is interrupted by the now closed valve member126. Thus, the hydraulic pressure in wheel cylinders 27 and 28 providedfor front wheels 25 and 26, respectively, is prevented from increasing.It will be clearly understood that when solenoid coil is againdeenergized by opening of switch 101, all the constituent parts arereturned to their shown position in FIG. 7.

A secondary differential signal generator adapted for sensing a possibleor already realized skid condition of automotive wheel or wheels andconstruct a modified DC motor is illustrated in FIG. 7. This device canbe replaced for the skid sensing arrangement shown in FIG. 4, whencombined with an electronic circuit shown in FIG. 16.

This device comprises a stationary field yoke 140 which is formed with adiametrally opposed pair of salient poles 141 and 142 and a pair ofwindings L1 and L2 wound around respective poles 141 and 142. Inputterminal 143 is electrically connected to the positive side of a DCcurrent source, not shown, and one end of said winding L1 is connectedto said terminal 143 by a lead 144 and the opposite end of winding L1 isconnected by a conductor 145 to one end of winding L2 the opposite endof which is connected to another source terminal 146 by means of a lead147. The winding direction of first winding L1 is same as that of secondwinding L2.

The field yoke 140 is further formed with a pair of salient poles 148and 149 which are provided each at an angular shift of 90 from theneighboring pole 141 or 142. These poles 148 and 149 are provided withrespective windings L3 and L4 which are wound in the same direction asbefore relative to each other and connected electrically with eachother, on the one hand, and to respective output terminals 150 and 151in the similar mode to that of former windings L1 and L2 which act asenergizing coils, while windings L3 and L4 act as sensing coils, as willbecome more clear as the description proceeds.

At the center of the yoke 140, there is provided a rotor 152 made of asuitable magnetizable material such as iron and operatively andmechanically connected with propeller shaft 40 or the rear wheel axle100 or the like, as will be easily supposed and thus not shown. Theouter cylindrical surface or rotor 152 is covered by conductor means 153fixedly attached thereto, although the fixing means have been omittedfrom the drawing only for simplicity.

When the vehicle is and thus its rear wheels are stopped and a DCcurrent is conveyed through series energizing coils L1 and L2, magneticfluxes emanate from first pole 141 through the rotor 152 toward theopposite pole 142.

When the rotor begins to rotate as shown by the full lined arrow, thepart of conductor 153 which is positioned opposite to first pole 141 isinduced with a current directing away from the viewer and perpendicularto the drawing paper, while in the part of the same conductor 153 whichis positioned opposite to second pole 142, a current is induced whichdirects towards the viewer and perpendicular to the drawing paper.

The voltage induced in the conductor 153 is directly proportional to therotational speed of the rotor and thus a primary differential of therotor speed. This induced current will generate magnetic fluxes whichdirect from the pole 149 towards the opposite pole 148, thuscross-linking the coils L4 and L3. So far as the rotational speed of therotor remains constant, the induced voltage in conductor 153 is alsoconstant and the density of the fluxes generated by the voltage willremain constant. So far as the rotor rotates at a constant speed, novoltage will appear at output terminals 150 and 151.

On the contrary, when the rotational speed of rotor 152 is changedsuddenly and substantially, the voltage induced in the conductor willvary abruptly, thus a potential difference appears between the outputterminals and said difference representing a kind of secondarydifferential. The thus developed voltage has naturally the positive ornegative sign, depending upon whether the speed change is acceleratingor decelerating, as the case may be. Therefore, it will be seen thatwith the rotor subjected acceleration or deceleration, a positive ornegative voltage appears in the sensing coil means.

The electronic circuit shown in FIG. 16 serves as a wheel skid controlmeans which comprises amplifier circuit 1, minimum signal level settingcircuit II, delay circuit III, temporary brake release signal circuit IVand constant voltage source circuit V, as shown by several dotted lineblocks.

When a deceleration should happen to take place in the rotationalmovement of rear wheels 32 and 33 to such a degree that these wheels areabout to skid or even brought into a skidded condition, the controlcircuit will act to reduce or even to release the braking force appliedto the rear wheels.

One of the output terminals at 151 of the modified motor 154 shown inFIG. 7 is connected electrically through condenser C12 with the baseelectrode of transistor T1, while another output terminal 150 isconnected to a source voltage line 155. Transistor T1 is biased byseveral resistors R11, R12, R13 and R14 so as to amplify only thedeceleration signal sensed by sensing coils L3 and L4. Condenser C11connected in parallel thereto acts as a filter which suppresses minordeceleration signals occasionally developed by rotational fluctuationsof the rotor 152 or minor speed changes in running of the automotiverear wheels from being amplified by the amplifier circuit I.

The deceleration signal amplified at transistor T1 is is applied throughresistor R15 to the base electrode of transistor T2, fitted withresistors R16 and R17, thereby being further amplified. The thusamplified signal is then fed from the collector electrode of transistorT2 trough a coupling condenser C13 to the minimum signal level settingcircuit 11. This second circuit constitutes a kind of Schmidt circuitcomprising transistors T3 and T4, resistors R18-R25 and condenser C14.Under normal conditions, transistor T3 is off, while transistor T4 ison. When a deceleration signal which is higher than a predeterminedvalue is applied to transistor T3, the latter turns on, while transistorT4 turns off. These operating conditions are maintained so far as theapplied signal remains higher than the set level. This pulse signal isconveyed from collector electrode of transistor T4 through diode D11 tothe third or delay circuit III which contains transistors T and T6,resistors R26-R31, condensers C and C16 and constitutes a monostablemultivibrator. Under normal conditions, transistor T5 is off, whiletransistor T6 is on.

So far as the deceleration voltage higher than the set signal level isapplied, transistor T4 turns off, while the collector potential oftransistor T4 remains equal to earth one and the collector potentialtransistor T5 approaches gradually to earth potential. By this reason,transistor T5 turns from off to on, while transistor T6 will turn fromon to off. These switched conditions will remain unchanged during thetime interval which depends upon the time constant provided by thecombination of condenser C15 with resistor R28. The output signaldelivered from this delay circuit is conveyed from the collectorelectrode of transistor T6 through the resistor R32 to the fourthcircuit or brake release signal circuit lV.

Transistors T7 and T8 constitute in combination a pulse signal amplifiercircuit adapted for amplifying the fed signal from the foregoing delaycircuit. When the transistor T6 turns from on to off, the collectorpotential will be lowered and the transistor T7 will turn on. In thisway, the emitter side potential at resistor R13 will be lowered. Whenthe base potential at transistor T8 is lowered, transistor T8 will turnon.

By this operation, the base potential at the switching transistor T9will increase and that transistor turns on. Therefore, valve controlcoil 64 connected in series between the collector electrode oftransistor T9 and source voltage line is fed with current, and at thesame time skid alarm lamp L connected in parallel with said coil 64'will be ignited, the diode at D12 connected in parallel with said coil64' serves for avoiding transistor T9 from being affected by thereversed electromotive force provided by said coil 64' which is similarto that shown in FIG. 1 in its general arrangement and func- 11011.

The fifth or constant voltage source circuit V is so designed andarranged to meet with possible variation in the source voltage ofbattery at 156, so as to assure a highly stabilized operation of theelectronic control circuit shown in FIG. 16.

As commonly known, the automotive accumulator battery is always chargedby an alternator fitted on the automotive vehicle, and therefore thesource voltage delivered from the battery contains more or less riples.The battery voltage will vary depending upon the occasional electricalload fluctuation on board of the vehicle. In the present embodiment, themore or less variable DC voltage is stabilized by the provision of chalkcoil L14 and condenser C17. In the similar way, the output signal isconveyed to solenoid coils 64 and 58, and so on.

In the second embodiment shown in FIG. 8, same or similar constituentparts as those employed in the first embodiment are denoted with samerespective reference numerals or symbols for easy comparison and betterunderstanding of the invention. As seen, the overall antiskid type brakesystem is so designed and arranged that the front wheel pair 25, 26 isarranged to be brought into an impending locked condition before therear wheel pair 32, 33. a

In the third arrangement known in FIG. 9, same or similar constituentparts as before are denoted with same reference numerals and symbols,yet attached each with a single prime for easy comparison and betterunderstanding of the present invention.

The main difference between the first and the third embodiments residessubstantially in that in the latter, the power piston of brake booster13 is utilized simultaneously as the similar piston employed in thereducing valve assembly 20, FIG. 1. The master cylinder 14' is just sameas shown in detail in FIG. 3.

The air change-off valve assembly 36' is shown in detail in FIG. 10.

In this assembly 36', there is provided a stationary main part which isformed with vacuum inlet 161 pneumatically connected with an enginesection manifold such as shown at 105 in FIG. 2. An outlet 162 is madeintegral with the main body part 160 and leads to inlet part 104 of thepneumatic booster assembly 13 shown in FIG. 2. Inlet 161 and outlet 162are normally kept in pneumatic communication through valve chamber 163when a slidable twin valve member 164 is positioned as shown in FIG. 10.An outlet piece 165 is screwed into the main body part 160 and formed atits innermost end with a valve seat 165a which is normally closed by thefirst valve element 166 so that otherwise established communicationbetween outlet bore 165b formed through said piece 165, on the one hand,and the outlet 162 through valve chamber 163, on the other hand, ispositively interrupted. There are further two valve seats 167 and 168 ofwhich the latter is closed normally by the second valve element 169 ofthe'twin valve member. A bored intermediate body part 170 is screwed tomain body part 160 adapted for slidable guidance of a perforated plunger171 which is linkedly connected at 172 with the inner end of the twinvalve member 164. To the intermediate body part 170, a hollow member 173is fixedly attached through connecting bushing 174 and positioning nut175. Around bushing 174 and hollow member 172, a solenoid coil 176 iswound and positioned rigidly by tightening said nut 175. The requiredpositioning in this respect is further assured by the provision of acylindrical cover 177 which houses substantial part of said solenoidcoil 176.

The port l65b is connected pneumatically through a suitable piping toinlet socket 178 shown in FIG. 2. Socket 178 kept in pneumaticcommunication with the interior of the variable pressure chamber 74 ispneumatically connected in turn with port 165.

The axial bore of the hollow member 173 is formed with an insideshoulder at 173a and the left-hand enlarged bore space l73b containing areturn spring 179 which urges the combined assembly of plunger 171 andtwin valve member 164 towards left in FIG. 10.

Main body part 160 is formed with an air port 180 which communicatesthrough air cleaner 181 with ambient atmosphere, on the one hand, and iskept in communication with passage 171a of plunger 171, on the otherhand.

When an output signal is delivered from the skid sensor 43 throughsignal processing circuit 45 to solenoid coil 176, plunger 171 togetherwith dual valve member 164 is moved rightwards in FIG. against theaction of return spring 179, valve elements 166 and 169 are brought intopressure contact with other side valve seat 167, and seat 171a onplunger 171, respectively. Thus, the outlet 162 is brought intocommunication through valve chamber 163, air port 180 and cleaner 181with the atmosphere. This introduced atmospheric air is supplied throughinlet socket 104 to the chamber 75 (FIG. 2).

With the aforementioned shift of first valve member 166, the valve seat165a is opened so that vacuum pressure is conveyed from inlet 161 tooutlet 165b, thence through inlet socket 178 into the related chamber74.

With the effective cooperation of second valve element 169 with valveseat 1710, pneumatic communication between air ports 180 and 173s isinterrupted, and therefore no atmospheric air is supplied to inlet port66, FIG. 2. Therefore, the pressure conditions of both chambers 74 and75 are changed. More specifically, the normally vacuum chamber 75accumulates now atmospheric pressure, while the variable pressurechamber 74 is kept in vacuo. The relative pressure conditions betweenboth chambers 74 and 75 are therefore reversed to those under the normalconditions, and thus power piston 70 is forced backwards or moreprecisely rightwards in FIG. 2 against the foot pedal pressure exertedby the vehicle driver intending to actuate the brake. This operationleads to lower the hydraulic brake pressure to the rear wheels, thuspreventing a wheel skid.

When the skid impending condition at the rear wheels is thus removed andthe skid sensor does not deliver any output signal, the solenoid coil176 is deenergized and all the working parts of the air pressurechange-off device, FIG. 10, are returned back to their normal positionshown.

The optionally employable brake or wheel cylinder pressure controldevice schematically shown at 185 in phantom lines is shown in FIG. 11more in detail.

This device 185 comprises a hollow cylinder 186 having an open end 1860is tightly closed by a closure member 187 through intermediary ofsealing means 188 by means of conventional fixing means such as screwconnection shown at 189. i

A piston consisting of a larger piston element 190a and a smaller pistonelement 190b is sealingly and reciprocably mounted within the interiorspace of said cylinder 186, the sealing means adapted for this purposebeing shown at 191 and 192. An oil chamber 193 containing a returnspring 194 is 2. defined by the cylinder wall and the smaller piston190b, said chamber being kept in hydraulic communication through conduit195 and connecting piping 19 (see, also FIG. 9) with a proper outputport of master cylinder 14 which port may be similar to that shown at 18in FIG. 1.

A further 011 chamber 196 is defined by the cylinder wall, large pistonelement 190a and closure member 187, said chamber 196 being kept inhydraulic communication through pipings 3040 and 31' to the rear wheelcylinders 34' and 35' which may be similar to those at 34 and 35 shownin FIG. 1.

A valve chamber 197 is formed in the body of closure member 187 andcontains substantial part of valve member 199 backed up by a returnspring 240, said chamber 197 being kept in hydraulic communication withthe junction at 241 between pipings 195 and 19'. Valve seat member 242is mounted fixedly in the closure member, said valve member being keptin physical separation from the valve seat member as shown.

In all the foregoing three embodiments, a selected pair of vehiclewheels, preferably rear wheels (except in the case of the arrangementshown in FIG. 8), is arranged to be brought into an impending lockedcondition before the remaining vehicle wheels, preferably front wheels.For this purpose, various measures can be adopted. In the firstembodiment, this is realized by adopting two different diameter pistons91b and 92b. With smaller piston 91b, high hydraulic pressure isdelivered from port 18 of master cylinder toward rear wheel brakecylinders 34 and 35. With larger piston 92b, low hydraulic pressure isdelivered from port 15 toward front wheel brake cylinders 27 and 28. Forthe similar purpose, the brake cylinder pistons for vehicle rear wheelscan be increased relative to those for front vehicle wheels.

The pressure control valve assembly shown in FIG. 11 well serves for thesame purpose.

In the operation of the pressure control assembly shown in FIG. 11, whenthe foot brake pedal similar to that denoted 10 in FIG. 1 is depressed,hydraulic master cylinder pressure is conveyed through piping 19 andconduit 198, valve chamber 197 and valve opening 242a into the cylinderspace 196 directly before the pressure receiving surface of largerpiston element a. In the similar way, the same hydraulic pressure isconveyed through piping 19 and conduit into hydraulic chamber 193. Onaccount of the difference in diametral dimensions of both larger andsmaller pistons, the piston will be hydraulically urged to moveleftwards in FIG. 11, thus compressing the return spring 194 andsimultaneously closing the valve opening 242a by valve member 199. Thus,the hydraulic pressure prevailing in the chamber 196 will start toreduce. When the thus accumulated energy in the spring plus thehydraulic pressure multiplied by the small piston area exceeds the thusreducing hydraulic pressure multiplied by the large piston area, thepiston will move in the reverse direction or more specificallyrightwards in FIG. 11, and thus the valve 199 reopens the valve opening242a so that the hydraulic pressure prevailing the larger piston chamber196 will soon recover the line or master cylinder pressure, and so on.In this way, the hydraulic piston will perform a reciprocating movementwith a certain higher frequency.

In practice, however, the piston reciprocating movement is not broughtabout at lower master cylinder pressures. In FIG. 13, a 45 inclinedstraight line X is plotted. With lower master pressures below thatcorresponding to a predetermined point Y on the line which point isdetermined by the piston area difference, front and rear wheel brakecylinders are supplied with equal hydraulic pressures. When the point Yis reached and the master pressure exceeds the correspondingpredetermined value, the curve will travel along that denoted with Z. Inpractice, this curve Z consists of that representing a infinitelynumerous minor undulations caused by the piston reciprocations. Thecurve S represents an ideal performance curve. When the practical curvelies above this ideal curve, the rear wheels will be brought into animpending skidding condition before the front wheels and are more liableto lock than the as at T lies below the ideal curve, the skidding may bemore liable to occur at the front wheels than the rear wheels in thepresent embodiment. The curve X-YZ is naturally caused to take placewith a sudden and heavy braking operation at foot pedal 10.

In the case of automotive trucks, however, a sudden braking mayfrequently invite a positional shift of the loaded baggages or the like.And thus, same braking effort may vary with increased or reducedhydraulic brake pressure. Therefore, it is preferable to control thehydraulic brake pressure depending to lesser or more degree of such loadshift.

Finally referring to FIGS. 12 and 14, a load-sensing brake pressurecontrol assembly 243 which can be positioned at 185 in FIG. 9 isillustrated in detail.

With this assembly 243, its upper hinge connection 244 is attached tothe vehicle chassis, partially shown at 245, in close proximity to theits regular suspension spring, not shown. A strong tension spring 246 istensioned between a channel 247 formed on the lower end of the assembly,and to the axle shaft such as at 100 in FIG. 1 by means of a properconventional attaching means such as bolt and nut at 248 in FIG. 12.

The main body of the assembly 243 comprises a main cylinder 249 and ahollow sleeve 250 fixedly screwed to the lower end thereof. At the lowerend of the sleeve, there is provided a perforated closing cap 251fixedly attached thereto. Within the interior space of the cylinder, adifferential piston 252 having a large piston element 252a and a smallpiston element 252b, a ring-shaped chamber 253 being formed therebetweenand kept in hydraulic communication through a port 254 with the mastercylinder. A head plug 255 is attached by screwing to the upper end ofsaid cylinder 249, on the one hand, and mechanically connected to thehinge 244, on the other hand. A hydraulic chamber 256 is formed betweenthe lower end of head plug 255 and the upper or pressure-receivingsurface of larger piston element 252a, said chamber 256 beinghydraulically connected with a valve 257 and its housing space orvalve'chamber 258. Chamber 256 is connected with the rear brakes througha passage 259 and a port 260. A bleed fitting 260 is attached to theupper end of head plug 255 and communicated with chamber 258 throughpassage 259. As seen, said valve, valve chamber and passage arecontained or housed in the head plug. The upper ball end 26la ofadjuster rod 261 is mechanically connected with the lower end of saiddifferential piston, said rod passing through said sleeve 250 and cap251 and screwed into an adjustable nut 262 which is formed with thespring-receiving channel 247. A strong compression spring 263 is housedin the sleeve 250 as shown.

It will be clearly understood that with increased loading, the distancebetween the upper and lower ends of the shown device will be shortenedand the compression degree of spring 263 is correspondingly accentuated,and vice versa. The length of tension spring 246 will be naturallyreduced in this case. The spring force of the compression spring 263 isso adjusted to provide specific oil pressure characteristic curves W1and W2 and the like which are very close to the ideal curve S1. Theupper curve Wl corresponds to a certain high load, while the lower curveW2 corresponds to a certain low load. The adjustment of the spring inthis embodiment is such that an impending locked condition will bebrought about in the rear wheels before an impending locked condition inthe front vehicle wheels when subjected to heavy braking.

When heavier braking pressure is applied to the footoperated brakepedal, pressure oil is conveyed from master cylinder through a pipingand the port 254 to chamber 253, thence through passages 264-266 andvalve chamber 258 to piston chamber 256. In the similar way as wasdescribed by reference to FIG. 11, the differential piston 252 willperform a frequently and rapidly repeated reciprocating movementdepending upon the differential piston area, the amount of the carriedload on the vehicle and the degree of deceleration of the vehicle causedby the application of the braking effort and thus the occasionalconditions of both springs 246 and 263.

Therefore, in this case, the closing and reopening frequency of thevalve 257 depends upon the above mentioned several parameters.

In this way, the passage of hydraulic liquid pressure coming from themaster cylinder and through the valved passage 266, passage 259 and portfitting 260, to the rear wheel brake cylinders such as 34 and 35, or 34'and 3 5' in FIG. 9 can be controlled depending upon the occasionallyloaded conditions of the vehicle.

Although several features have been separately described in theforegoing several specific embodiments, it will be stressedly understoodthat aforementioned separate constructional features in a certainembodiment may be well combined with other features shown and describedin any of other embodiments in the foregoing.

In practice, however, the rear wheels may be locked only for a shorttime interval even when using the arrangement embodying the principlesof the invention. Such a phenomenon may be tolerated when the skiddedconditions extend for a highly limited time period.

What we claim is:

1. An automotive brake system for a vehicle having at least two pairs ofrunning wheels, each wheel of said running wheel pairs including a brakeassembly having a hydraulic actuating cylinder, a hydraulic pressuresupply :means for actuating said wheel brake assemblies, a first conduitmeans'communicating said pressure supply means to the brakes of one ofsaid wheel pairs, a second conduit means communicating said hydraulicpressure supply means with the brakes of the other of said wheel pairs,means for bringing about an impending locked condition in the other ofsaid wheel pairs prior to bringing about an impending locked conditionin said one of said wheel pairs, skid sensing means operativelyconnected with said other of said wheel pairs for creating a signal inresponse to sensing an impending skidding condition of said other ofsaid wheel pairs, cutoff valve means connected in said first conduitmeans for blocking the flow of hydraulic pressure applied by said firstconduit means for blocking the flow of hydraulic pressure applied bysaid hydraulic pressure supply means to said one of said wheel pairs,reducing, valve means connected in said second conduit means forinterrupting the flow of hydraulic pressure from said hydraulic pressuresupply means to said other of said wheel pairs and increasing the volumeof said conduit to reduce the pressure applied to said other wheelpairs, and control means interconnecting said skid sensing means withsaid cutoff valve means and said reducing valve means for actuating saidcutoff valve: means to maintain the hydraulic pressure at said one ofsaid wheel pairs and simultaneously actuating said reducing valve meansto allow a decrease in the hydraulic pressure applied to said other ofsaid wheel pairs upon the sensing of an impending skid condition by saidskid sensing means, whereby the hydraulic pressure applied to said otherof said wheel pairs is reduced while the pressure applied to said one ofsaid wheel pairs is maintained to allow said other of said wheel pairsto rotate while maintain ing a constant braking effect on the wheels ofsaid one of said wheel pairs.

2. An automotive brake system as claimed in claim 1, wherein saidhydraulic pressure cutoff means located in said first conduit meansbetween said hydraulic pressure supply means and said one of said wheelpairs is comprised of a valve body, a first hydraulic passage connectedbetween said hydraulic pressure supply means and said valve body, asecond hydraulic passage connected between said valve body and saidwheel brake cylinders, a chamber in said valve body connecting saidfirst and second passages, a valve member and said second passage tourge said valve member in a closing direction, an electric solenoidassembly, including a plunger, located on that end of said valve bodythat is opposite to said second passage, a reciprocating stem slidablyguided between said valve member and said plunger of said electricsolenoid, a spring for urging said plunger, said stem, and said valvemember in an open direction, whereby when said electric solenoid isactuated by said control means, said plunger will move against the forceof said spring urging said valve means in the open direction, therebyallowing said valve member to move to the closed position and cut offthe flow of hydraulic fluid from said hydraulic pressure supply means tosaid wheel brake cylinders to prevent a further increase in the pressureapplied to the wheel brake cylinders of said first wheel pair.

3. An automotive brake system as claimed in claim 1, wherein saidreducing valve means comprises, an incoming hydraulic conduit connectedto said hydraulic pressure supply means, an outlet conduit connected tothe wheel brake cylinders of said other of said wheel pairs, a passageconnecting said inlet conduit and said outlet conduit, a valve meanslocated in said passage for selectively blocking communication of saidinlet passage with said outlet passage, a plunger movably positioned insaid chamber between said valve means and the wheel brake cylinders ofsaid other of said wheel pairs for varying the volume of said passage, apneumatic servo motor means operatively connected with said valve meansand said plunger, said servo motor means having a sealed cavity therein,a diaphragm piston dividing said cavity into a first and a second sealedchamber, said diaphragm piston being operatively connected with saidplunger and said valve means, a first pneumatic conduit means forpneumatically communicating said first and second chambers with eachother, a second pneumatic conduit means communicating said second sealedchamber with a source of pneumatic vacuum, and a changeoff valve meansconnected in said first pneumatic conduit means, said change-off valvehaving a first position for communicating said first chamber with saidsecond chamber and a second position for blocking said first pneumaticconduit means and communicating said first chamber with the ambientatmosphere, said change-off valve being actuated by said control meansupon the sensing of a skid condition by said skid-sensing means to blockthe communication of said first chamber with said second chamber andintroduce ambient atmospheric air into said first chamber to actuatesaid valve means to block the flow of hydraulic pressure from saidhydraulic pressure supply means to said wheel brake cylinders andincrease the volume between'said valve means and said wheel brakecylinders, whereby the wheel brake actuating pressure is reduced toallow rotation of the wheels of said other wheel pair.

4. An automotive brake system as claimed in claim 1, further comprising,a pneumatic booster assembly operatively connected with said hydraulicpressure supply means to provide a power assist therefor, said pneumaticbooster assembly including a sealed cavity therein, said cavity dividedinto a first and a second chamber by a diaphragm piston means, saiddiaphragm piston being operatively connected with said hydraulicpressure supply means for the actuation thereof, said first chamberbeing connected with a source of vacuum, a first pneumatic conduitcommunicating said chamber with said second chamber, and an airchange-off valve means connected in said second pneumatic conduit means,said changeoff valve having a first position and a second position, saidfirst position for communicating said first chamber of said pneumaticbooster with said vacuum source and said second position forcommunicating ambient atmosphere to said first chamber and connectingsaid second chamber with said vacuum source, said change-off valve meansbeing actuated by said control means in response to a sensed skidcondition by said skid-sensing means, whereby said cut-off valve isactuated and said air change-off valve causes said pneumatic booster todecrease the amount of hydraulic pressure supplied to the brakes of saidother wheel pairs by said hydraulic pressure supply means to allow saidwheels of said other wheel pair to rotate.

5. An automotive brake system as claimed in claim 1 further stegped boretherein, a stepped piston slidably positioned in sai stepped bore, saidstepped piston having a smaller diameter portion communicating with saidhydraulic pressure supply means and a larger piston portioncommunicating with the actuating cylinders of said other of said wheelpairs, a conduit communicating said smaller diameter portion of saidstepped piston with said larger diameter portion thereof, a valve meanslocated in said interconnecting conduit and operatively connected withsaid stepped piston, a biasing means for biasing said valve means in anopen position, whereby, when hydraulic pressure is applied by saidhydraulic pressure supply means, said stepped piston is caused toreciprocate to allow the pressure supplied to the wheel brake assembliesof said other of said wheel pairs to increase step-wise.

6. An automotive brake system as claimed in claim 1, further comprisinga load sensing valve means connected in said second conduit means, saidload sensing valve means including a stepped piston slidably positionedin a cylinder said stepped piston having a smaller diameter portion anda larger diameter portion formed thereon, an interconnecting conduitcommunicating the portion of said cylinder containing said largerdiameter portion of said piston with the cylinder portion containing thesmaller diameter portion of said piston, said smaller diameter portionof said piston communicating with said hydraulic pressure supply means,a valve means located in said interconnecting passage and operativelyconnected with said piston assembly to selectively block communicationof said smaller diameter piston portion with said larger diameter pistonportion, a first biasing means for biasing said valve means in an openposition, said load sensing valve means being connected between a loadsupporting sprung portion and an unsprung portion of a vehicle through asecond biasing means, said second biasing means acting in opposition tosaid first biasing means, whereby, as the vehicle loads increase, saidfirst biasing means moves said valve means towards its open position,thereby allowing reciprocable movement of said stepped piston to causethe hydraulic pressure applied to the wheel brakes of the other of saidwheel pairs to increase step-wise as the vehicle load is increased.

7. An automotive brake system as claimed in claim 1, said control meanscomprising a self-holding circuit means including a sloenoid and aswitching means, said solen'oid being operatively connected with saidskid sensing means to hold said switching means in a closed positionduring operation of said sensing means, said switching means operativelyconnected with said cut-off valve means to control the actuationthereof, and further including a second switching means for controllingthe operation of said solenoid, said second switching means actuated inresponse to a signal created by said skid means.

8. An automotive brake system as claimed in claim 1, wherein said skidsensing means comprises, a direct current generator having an armatureoperatively connected to said other wheel pairs and having the windingof a field yoke connected to said control means for actuating saidcontrol means when said generator ceases to generate an electric currentwhen said other wheel pairs are locked in a skid condition.

1. An automotive brake system for a vehicle having at least two pairs ofrunning wheels, each wheel of said running wheel pairs including a brakeassembly having a hydraulic actuating cylinder, a hydraulic pressuresupply means for actuating said wheel brake assemblies, a first conduitmeans communicating said pressure supply means to the brakes of one ofsaid wheel pairs, a second conduit means communicating said hydraulicpressure supply means with the brakes of the other of said wheel pairs,means for bringing about an impending locked condition in the other ofsaid wheel pairs prior to bringing about an impending locked conditionin said one of said wheel pairs, skid sensing means operativelyconnected with said other of said wheel pairs for creating a signal inresponse to sensing an impending skidding condition of said other ofsaid wheel pairs, cutoff valve means connected in said first conduitmeans for blocking the flow of hydraulic pressure applied by said firstconduit means for blocking the flow of hydraulic pressure applied bysaid hydraulic pressure supply means to said one of said wheel pairs,reducing valve means connected in said second conduit means forinterrupting the flow of hydraulic pressure from said hydraulic pressuresupply means to said other of said wheel pairs and increasing the volumeof said conduit to reduce the pressure applied to said oTher wheelpairs, and control means interconnecting said skid sensing means withsaid cutoff valve means and said reducing valve means for actuating saidcutoff valve means to maintain the hydraulic pressure at said one ofsaid wheel pairs and simultaneously actuating said reducing valve meansto allow a decrease in the hydraulic pressure applied to said other ofsaid wheel pairs upon the sensing of an impending skid condition by saidskid sensing means, whereby the hydraulic pressure applied to said otherof said wheel pairs is reduced while the pressure applied to said one ofsaid wheel pairs is maintained to allow said other of said wheel pairsto rotate while maintaining a constant braking effect on the wheels ofsaid one of said wheel pairs.
 2. An automotive brake system as claimedin claim 1, wherein said hydraulic pressure cutoff means located in saidfirst conduit means between said hydraulic pressure supply means andsaid one of said wheel pairs is comprised of a valve body, a firsthydraulic passage connected between said hydraulic pressure supply meansand said valve body, a second hydraulic passage connected between saidvalve body and said wheel brake cylinders, a chamber in said valve bodyconnecting said first and second passages, a valve member and saidsecond passage to urge said valve member in a closing direction, anelectric solenoid assembly, including a plunger, located on that end ofsaid valve body that is opposite to said second passage, a reciprocatingstem slidably guided between said valve member and said plunger of saidelectric solenoid, a spring for urging said plunger, said stem, and saidvalve member in an open direction, whereby when said electric solenoidis actuated by said control means, said plunger will move against theforce of said spring urging said valve means in the open direction,thereby allowing said valve member to move to the closed position andcut off the flow of hydraulic fluid from said hydraulic pressure supplymeans to said wheel brake cylinders to prevent a further increase in thepressure applied to the wheel brake cylinders of said first wheel pair.3. An automotive brake system as claimed in claim 1, wherein saidreducing valve means comprises, an incoming hydraulic conduit connectedto said hydraulic pressure supply means, an outlet conduit connected tothe wheel brake cylinders of said other of said wheel pairs, a passageconnecting said inlet conduit and said outlet conduit, a valve meanslocated in said passage for selectively blocking communication of saidinlet passage with said outlet passage, a plunger movably positioned insaid chamber between said valve means and the wheel brake cylinders ofsaid other of said wheel pairs for varying the volume of said passage, apneumatic servo motor means operatively connected with said valve meansand said plunger, said servo motor means having a sealed cavity therein,a diaphragm piston dividing said cavity into a first and a second sealedchamber, said diaphragm piston being operatively connected with saidplunger and said valve means, a first pneumatic conduit means forpneumatically communicating said first and second chambers with eachother, a second pneumatic conduit means communicating said second sealedchamber with a source of pneumatic vacuum, and a change-off valve meansconnected in said first pneumatic conduit means, said change-off valvehaving a first position for communicating said first chamber with saidsecond chamber and a second position for blocking said first pneumaticconduit means and communicating said first chamber with the ambientatmosphere, said change-off valve being actuated by said control meansupon the sensing of a skid condition by said skid-sensing means to blockthe communication of said first chamber with said second chamber andintroduce ambient atmospheric air into said first chamber to actuatesaid valve means to block the flow of hydraulic pressure from saidhydraulic pressure supply means to said wheel brake cylinders andincreaSe the volume between said valve means and said wheel brakecylinders, whereby the wheel brake actuating pressure is reduced toallow rotation of the wheels of said other wheel pair.
 4. An automotivebrake system as claimed in claim 1, further comprising, a pneumaticbooster assembly operatively connected with said hydraulic pressuresupply means to provide a power assist therefor, said pneumatic boosterassembly including a sealed cavity therein, said cavity divided into afirst and a second chamber by a diaphragm piston means, said diaphragmpiston being operatively connected with said hydraulic pressure supplymeans for the actuation thereof, said first chamber being connected witha source of vacuum, a first pneumatic conduit communicating said chamberwith said second chamber, and an air change-off valve means connected insaid second pneumatic conduit means, said change-off valve having afirst position and a second position, said first position forcommunicating said first chamber of said pneumatic booster with saidvacuum source and said second position for communicating ambientatmosphere to said first chamber and connecting said second chamber withsaid vacuum source, said change-off valve means being actuated by saidcontrol means in response to a sensed skid condition by saidskid-sensing means, whereby said cut-off valve is actuated and said airchange-off valve causes said pneumatic booster to decrease the amount ofhydraulic pressure supplied to the brakes of said other wheel pairs bysaid hydraulic pressure supply means to allow said wheels of said otherwheel pair to rotate.
 5. An automotive brake system as claimed in claim1 further comprising a pressure control valve means, said pressurecontrol valve means connected in said second conduit means, saidpressure control valve means including a housing having a stepped boretherein, a stepped piston slidably positioned in said stepped bore, saidstepped piston having a smaller diameter portion communicating with saidhydraulic pressure supply means and a larger piston portioncommunicating with the actuating cylinders of said other of said wheelpairs, a conduit communicating said smaller diameter portion of saidstepped piston with said larger diameter portion thereof, a valve meanslocated in said interconnecting conduit and operatively connected withsaid stepped piston, a biasing means for biasing said valve means in anopen position, whereby, when hydraulic pressure is applied by saidhydraulic pressure supply means, said stepped piston is caused toreciprocate to allow the pressure supplied to the wheel brake assembliesof said other of said wheel pairs to increase step-wise.
 6. Anautomotive brake system as claimed in claim 1, further comprising a loadsensing valve means connected in said second conduit means, said loadsensing valve means including a stepped piston slidably positioned in acylinder said stepped piston having a smaller diameter portion and alarger diameter portion formed thereon, an interconnecting conduitcommunicating the portion of said cylinder containing said largerdiameter portion of said piston with the cylinder portion containing thesmaller diameter portion of said piston, said smaller diameter portionof said piston communicating with said hydraulic pressure supply means,a valve means located in said interconnecting passage and operativelyconnected with said piston assembly to selectively block communicationof said smaller diameter piston portion with said larger diameter pistonportion, a first biasing means for biasing said valve means in an openposition, said load sensing valve means being connected between a loadsupporting sprung portion and an unsprung portion of a vehicle through asecond biasing means, said second biasing means acting in opposition tosaid first biasing means, whereby, as the vehicle loads increase, saidfirst biasing means moves said valve means towards its open position,thereby allowing reciprocable movement of said stepped piston tO causethe hydraulic pressure applied to the wheel brakes of the other of saidwheel pairs to increase step-wise as the vehicle load is increased. 7.An automotive brake system as claimed in claim 1, said control meanscomprising a self-holding circuit means including a sloenoid and aswitching means, said solenoid being operatively connected with saidskid sensing means to hold said switching means in a closed positionduring operation of said sensing means, said switching means operativelyconnected with said cut-off valve means to control the actuationthereof, and further including a second switching means for controllingthe operation of said solenoid, said second switching means actuated inresponse to a signal created by said skid means.
 8. An automotive brakesystem as claimed in claim 1, wherein said skid sensing means comprises,a direct current generator having an armature operatively connected tosaid other wheel pairs and having the winding of a field yoke connectedto said control means for actuating said control means when saidgenerator ceases to generate an electric current when said other wheelpairs are locked in a skid condition.